Advance of technology has made all kinds of electronic devices (such as mouse) smaller. Electronic elements required by those electronic devices also have to be miniaturized. In the electronic devices, switch is the commonly used electronic element to transmit signals.
References for micro switch are seen in numerous prior arts, such as R.O.C. patent Nos. M350087, 507921 and 289485. R.O.C. patent No. M350087 discloses a micro switch including a housing, a common terminal, a normally-closed terminal, a normally-open terminal, a movable contact plate, a tension spring, a pushbutton and a pressing plate. The pressing plate has a dovetail portion to increase the force receiving area of the housing from the pressing plate to avoid the housing from being pierced through. In addition, the tension spring improves control of received force of the movable contact plate to obtain uniform and agile action force, thereby to further enhance performance and reliability of the movable contact plate.
R.O.C. patent No. 507921 also discloses a micro switch including an upper body and a lower body coupled together, a conduction contact and a fixed contact surface on the top of the lower body, an action member with a fixed end anchored on the fixed contact surface and a movable end fastened to a contact element. When a press element is pressed, the bottom thereof is to push the action member. The movable end of the action member is moved accordingly to allow the contact element to contact with the conduction contact to achieve switch function.
R.O.C. patent No. 289485 discloses a micro switch with a detent rib that has a cap with two protrusive rectangular ribs on the surface to control depression movement of the switch to improve durability.
While all the aforesaid prior arts have varying objectives and functions, they have a common feature. Referring to FIG. 1, a micro switch is provided and similar to the micro switches disclosed in the aforesaid prior arts. The micro switch includes a base 30 which has a common terminal 31, a normally-closed terminal 33 and a normally-open terminal 32 located thereon. The common terminal 31 is coupled with a conductive reed 34 which contacts with the normally-closed terminal 33 in normal conditions. When being depressed, the conductive reed 34 contacts with the normally-open terminal 32 to achieve switch function.
However, when the micro switch is installed on an electronic device, the conductive reed 34 is moved up and down to contact with the normally-closed terminal 33 and normally-open terminal 32, and generates discharge and arc to fuse the contact, thus carbon residues are produced and sprayed around. Since the sprayed carbon residues contain metal powders, they are accumulated after a period of time to form a conductive layer 35 connected to the normally-closed terminal 33 and normally-open terminal 32. The normally-closed terminal 33 and normally-open terminal 32 are set ON to cause failure of the micro switch during safety high voltage test, and also cannot pass safety approval of higher ampere. Production yield also is decreased.